A major limitation of cell therapies, such as allogeneic bone marrow transplantations or adoptive T cell therapy for cancer, is the rapid decline in viability and function of transplanted cells. Following cell transfer, therapeutic cells often rely on the co- delivery of adjuvant drugs, designed to maximize donor cell efficacy and in vivo persistence. Examples include administration of cytokines, including interleukin (IL-) 2, IL-7, IL-21 and IL-15 in adoptive T-cell therapy, or the use of small-molecule drugs to boost immune reconstitution following hematopoietic stem cell (HSC) transplants. However, these agents often require high and sustained systemic doses to achieve the desired therapeutic effect, leading to dose-limiting toxicities due to the generally pleiotropic nature of these drugs, which has restricted their clinical use. We propose a strategy for adjuvant drug delivery in cell therapies, based on chemical conjugation of submicron-sized drug-loaded synthetic particles directly onto the plasma membrane of donor cells prior to infusion into the patient, to permit continuous pseudo-autocrine stimulation of transferred cells in vivo. We hypothesize that that therapeutic HSCs or T cells "armed" with adjuvant drug- loaded particles exhibit greatly enhanced functionality using small doses of adjuvant drugs that have no substantial effect when given systemically. We will test our hypothesis in a mouse melanoma tumor model of adoptive T cell therapy and a murine transplantation model of HSC engraftment and reconstitution. PUBLIC HEALTH RELEVANCE: We will devise a facile and generalizable strategy to robustly augment the therapeutic potential of existing cell therapies, such as bone marrow transplantation or infusion of tumor-reactive T lymphocytes. If successful, a large variety of immune stimulants, which cause serious side effects when infused intravenously, can be safely targeted to therapeutically relevant cells and tissue.